The electric parts and auxiliary machines of the car and motors of industrial machines are demanded to be compact and have high performance and output year by year. Thus use conditions have become strict. The rolling bearing is used therefor. The grease composition is used to lubricate the rolling bearing. Because the use condition such as a high-speed rotation at high temperatures for the rolling bearing has become strict, there is a fear that a peculiar peeling phenomenon occurs with the rolling surface of the rolling bearing turning into white in its texture.
Unlike peeling which occurs from the inside of the rolling surface owing to normal metal fatigue, the peculiar peeling phenomenon is a destruction phenomenon which occurs from a comparatively shallow portion of the rolling surface. This is considered peeling owing to hydrogen brittleness owing to hydrogen generated caused by decomposition of the grease composition. As methods of preventing the peculiar peeling phenomenon from occurring in an early stage with the rolling surface turning into white in its texture, the method of adding a passivating agent to the grease composition is known (see patent document 1). The method of adding bismuth dithiocarbamate to the grease composition is also known (see patent document 2).
In recent years, there is a tendency for general-purpose motors such as an AC motor, a DC motor, and the like to be made smaller. As a result, bearings supporting rotors of motors tend to be operated at a higher speed and under a higher surface pressure. The grease composition is packed in these motors to impart lubricating property thereto. The grease composition is obtained by kneading a base oil, a thickener, and an additive as necessary. As the base oil, synthetic lubricating oil such as mineral oil, ester oil, silicone oil, and ether oil is generally used. As the thickener, a metal soap such as a lithium soap and urea-based compounds are generally used. As the additive, an antioxidant, a rust proof agent, a metal deactivator, a viscosity index improver, and the like are used.
To improve the high-temperature durability of the lubricating oil and the grease composition for use in a bearing and the like, as the antioxidant, organic zinc compounds such as zinc alkyldithiophosphate and amine compounds such as alkylated diphenylamine are used singly or in combination.
Bearings for motors for use in home electrical appliances and industrial equipment are used in a high temperature and speed rotation and demanded to be excellent in quietness and durability in high temperatures and high speeds. As the grease composition which is excellent in the high-temperature durability, suppresses abnormal noise when it is cold, and excellent in a peeling resistance property at a high temperature and under a high load, a composition composed of a base oil consisting of synthetic hydrocarbon oil and ester oil and a urea-based thickener added to the base oil is known (see patent documents 3 and 4). As a lubricating composition having along life until before seizing occurs in a high temperature and speed rotation condition, a composition containing ester oil as its base oil and 3 to 30 wt % of a thickener essentially containing an aliphatic diurea compound (see patent document 5) is known.
A propeller shaft for an FR car and a 4WD car couples a transmission side and a differential gear side to each other. A universal joint is provided at a proper position between the transmission side and the differential gear side. As a lubricant for the universal joint, grease for a wheel bearing and general-purpose grease have been used more than other kind of lubricants.
An electromagnetic clutch, an alternator, a flywheel damper which are electric parts and auxiliary machines are heated to high temperatures. Therefore as grease compositions to be packed in the rolling bearing for the electric parts and auxiliary machines, urea-based grease is generally used. As a grease composition to be packed in the rolling bearing for a fan clutch which is heated to an ultra-high temperature in the neighborhood of 200° C., fluorine grease using fluororesin particles as its thickener and perfluoropolyether oil as its base oil is used.
A heat roller of a copying machine heats toner composed of thermoplastic resin and a coloring agent to fix the melted toner to paper surface under pressure. Therefore the rolling bearing supporting the heat roller into which a heated is inserted is heated to ultra-high temperatures in the neighborhood of 200° C. Thus the fluorine grease is packed in the rolling bearing supporting the heat roller.
A ball bearing (see patent document 6) in which the grease composition containing the fluorine oil and the oil which has a lower specific gravity than the fluorine oil and does not mix with the fluorine oil as its base oil is packed. A grease composition (see patent document 7) using aromatic ester, polyphenyl ether, alkylated polyphenyl ether, ester oil, and perfluoro-polyalkyl ether oil as its base oil, dicarbamide as its thickener, PTFE and polyimide as its solid lubricant, and the additive generally used is also known.
Generally as the lubricant for the bearing, the lubricating oil composition or the grease composition is used more than other kind of lubricants. As the base oil contained in the lubricating oil composition or the grease composition as the main component thereof, synthetic oil such as mineral oil, poly-α-olefin (hereinafter referred to as PAO) oil, ester oil, silicone oil, and fluorine oil are used. In recent years, from the standpoint of energy saving, the lubricating oil composition or the grease composition for the bearing is demanded to have low friction and viscosity. As described above, with an increase in the demand for the development of the bearing which is compact and has high performance, there is a growing demand that the lubricant to be packed in the bearing has improved durability at high temperatures.
As a technique suggesting the possibility of a solution for the demand, for example, a fluid bearing apparatus (see patent document 8) using the lubricant to which the ionic liquid is added as the conductivity-imparting agent is known. The grease composition (see patent document 9) composed of the base oil containing the ionic liquid and the thickener is also known. In the above-described lubricant and grease composition, the property of the ionic liquid which is an ambient temperature molten salt has a low viscosity owing to the combination of various organic ions is utilized.
Many bearings for rotatably supporting rotating parts such as a photosensitive drum and various kinds of rollers are used for a copying machine and a printer. The photosensitive drum forms an electrostatic latent image on its surface to which electrically charged toner is attached to transfer a toner image to paper. Because high rotation accuracy is demanded in the field of an electrophotographic apparatus, a rolling bearing has been used. But the rolling bearing has a large number of parts. Thus application of inexpensive sliding bearings has been attempted for an economic reason. As such a sliding bearing, an oil-impregnated sintered bearing is exemplified.
Lubricating oil is impregnated into pores of a sintered molded bearing and held thereby and oozed out to the sliding surface of the oil-impregnated sintered bearing when it is used to allow it to have a stable frictional property for a longtime.
The sintered molded bearing is obtained by performing compression molding of fine particles of iron, copper, zinc, tin, graphite, nickel or mixing fine particles of these metals with each other to form an alloy, and performing compression molding of the alloy, firing, and sizing. The sintered molded bearing has a uniform porous tissue.
As the lubricating oil impregnated into the sintered molded bearing, synthetic lubricating oil (see patent document 10) such as mineral oil, diester oil, PAO oil, and ether oil is known.
The oil-impregnated sintered bearing composed of the above-described materials is less expensive than the rolling bearing in its production cost. Therefore the oil-impregnated sintered bearing is spreading in its utilization range as the bearing applicable to use in a high-temperature atmosphere inside the copying machine, the printer, and the like because recently the copying machine, the printer, and the like have become compact and have high performance such as high-speed printing.
A rolling bearing (see patent document 11) in which fluorine grease is packed and a sliding bearing (see patent document 12) using polyphenylene sulfide resin and polyimide resin have been used in the high-temperature atmosphere.